Ureammol/L
Protein-waste clearance
Also known as: BUN, Blood Urea Nitrogen
Typical optimal range
2.5–7.8 mmol/L
A commonly cited optimal range is 2.5–7.8 mmol/L, though reference intervals vary between laboratories, so your result should always be interpreted alongside the range provided on your report. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of kidney function markers, including urea, follows NHS and NICE guidance on chronic kidney disease (NICE guideline NG203) and standard laboratory medicine practice as outlined by the Association for Clinical Biochemistry.
What is Urea?
Urea is a waste product formed in the liver when the body breaks down proteins from food and from normal cell turnover. It travels through the bloodstream to the kidneys, which filter it out into urine. Measuring blood urea gives a useful snapshot of how well the kidneys are clearing this nitrogen waste, and can also reflect hydration status and dietary protein intake.
What a high Urea means
A raised urea level is a signal that the body is producing more urea than usual, clearing it less efficiently, or both — it prompts a closer look rather than pointing to a single cause straightaway.
- Dehydration. When fluid intake is low or losses are high (through sweating, vomiting, or diarrhoea), blood becomes more concentrated and urea rises. This is one of the most common and easily reversible reasons for a mildly elevated result.
- High protein intake. A very high-protein diet increases the nitrogen load the liver processes, producing more urea. This is generally a benign cause but worth considering if you eat a large amount of meat, protein supplements, or follow a high-protein diet plan.
- Kidney impairment or GI bleeding. Reduced kidney filtration — from acute illness or chronic kidney disease — allows urea to accumulate in the blood. A bleed anywhere in the gastrointestinal tract can also raise urea significantly, as the blood protein is digested and absorbed like dietary protein.
Urea is most informative when read alongside creatinine and eGFR; a raised urea with a normal creatinine often points to dehydration or diet rather than kidney disease.
What a low Urea means
A low urea level is less commonly a cause for concern, but can occasionally reflect reduced protein intake, an underlying liver issue, or excess fluid in the body.
- Low protein intake. Strict calorie restriction, a very low-protein diet, or poor nutritional intake can reduce the amount of nitrogen waste being produced, leading to lower-than-expected urea levels.
- Liver disease. Because urea is synthesised in the liver, significant liver impairment can reduce the liver's ability to produce it, resulting in low blood urea — this is usually seen alongside other abnormal liver markers.
Mild or borderline low urea in an otherwise healthy person with normal other markers is not usually clinically significant on its own.
Should I be worried?
A single urea result outside the reference range, particularly a mild deviation, is rarely cause for alarm on its own. Many everyday factors — a hot day, a high-protein meal before the test, or not drinking enough water — can shift the result. If your urea is raised, your GP will usually look at it alongside creatinine and eGFR to get a fuller picture of kidney function; they may also consider your hydration, recent diet, and any symptoms. A persistently elevated urea across repeat tests, especially with a falling eGFR or rising creatinine, would prompt further investigation. If you have symptoms such as persistent fatigue, swelling, or changes in urination, it is worth booking a GP appointment rather than waiting.
What actually helps
Keeping urea in a healthy range is largely about supporting your kidneys with good hydration and a balanced approach to protein intake.
- Stay well hydrated. Drinking adequate fluid — around 6–8 glasses of water or low-sugar drinks per day as a general guide — helps the kidneys dilute and excrete urea efficiently and is one of the most direct influences on the result.
- Balance protein intake. Protein is essential and should not be cut unnecessarily, but consistently very high intakes (particularly from red meat and supplements) increase the urea load. Aiming for a varied, moderate protein intake in line with general healthy eating guidance is a sensible approach.
- Manage blood pressure and blood sugar. High blood pressure and poorly controlled blood sugar are the leading causes of kidney damage in the UK; addressing these through diet, exercise, and medication where prescribed protects long-term kidney filtration capacity.
- Limit alcohol. Alcohol has a mild diuretic effect and, in excess, can impair both liver and kidney function, both of which influence urea levels.
There is good supporting evidence that certain dietary patterns help maintain healthy kidney function and keep urea production balanced.
Water and low-sugar fluids
Adequate hydration is the single most direct dietary lever for urea; it supports renal perfusion and urea excretion.
Vegetables and fruit
A diet rich in plant foods provides protein at lower amounts and with less nitrogen load than animal sources, supporting kidney health as part of an overall balanced diet.
Wholegrains
Wholegrains contribute fibre and micronutrients without adding a large protein or nitrogen burden, and are associated with better cardiometabolic and kidney health outcomes.
Oily fish
Omega-3 fatty acids from oily fish (salmon, mackerel, sardines) are associated with reduced inflammation and modest cardiovascular benefits that indirectly support kidney health.
Legumes and pulses
Beans, lentils, and chickpeas provide protein with a lower nitrogen load per gram than red meat and are a kidney-friendly protein swap supported by dietary research.
Track your own Urea
Upload a lab PDF and Better Days trends Urea over time, flags it when it drifts, and suggests foods that help.
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Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.